Japan's Retail Currency Traders Lose Clout

By

Tatsuo Ito

Updated Feb. 28, 2012 10:32 a.m. ET

TOKYO—Japanese retail currency investors, once famed for their contrarian trades and outsize impact on the market, appear to be losing some of their clout, hit by a combination of tighter margin regulations and a change in trading strategies prompted by the yen's persistent rise last year.

According to a survey conducted by industry bodies in April 2011, retail investors—often referred to collectively as "Mrs. Watanabe"...